1. Field of the Invention
The present invention relates to a method for quantifying the initial nucleic acid concentration, and more particularly, to a method for quantifying the initial nucleic acid concentration from real-time nucleic acid amplification data, which is obtained by polymerase chain reaction (PCR), ligase chain reaction (LCR), strand displacement amplification (SDA), nucleic acid sequence-based amplification (NASBA), transcription mediated amplification (TMA), rolling-circle amplification (RCA), and so on.
2. Description of the Related Art
Polymerase chain reaction (PCR) is most widely used among a variety of analysis methods for detecting and quantifying nucleic acid. A principle of the PCR is disclosed in U.S. Pat. Nos. 4,683,195 and 4,683,202.
Conventional PCR gives only a qualitative result of an amplified DNA at end point by an agarose gel. However, such conventional PCR has a problem in that it cannot be used in quantitative analyses. In order to solve the problem, real-time PCR has been developed. The real-time PCR uses an optical detection system to detect in real time the fluorescence intensity that is proportional to the concentration of an amplified DNA, such that a quantitative analysis of DNA is possible.
Conventional methods for quantifying the initial concentration of a nucleic acid from a nucleic acid amplification data are disclosed in U.S. Pat. Nos. 6,303,305 and 6,503,720. In these conventional methods, a nucleic acid is amplified and a function representing the amount of the nucleic acid in each amplification cycle is obtained. Then, n-th order derivative of the function is calculated and the initial concentration of the nucleic acid is calculated from the result. Also, a quantitative analysis method using the maximum value of the derivative as threshold cycle (Ct) is disclosed in U.S. Pat. No. 6,303,305, and a quantitative analysis method using maximum, minimum and zero value of the derivative as Ct is disclosed in U.S. Pat. No. 6,503,720.
Also, another method for quantifying the initial concentration of a nucleic acid from the nucleic acid amplification data is disclosed in U.S. Patent Application Publication No. 2002-0031768. Herein, the concentration of the nucleic acid is quantified using a specific value of the derivative.